WO2008145389A2

WO2008145389A2 - Vam shell catalyst, method for producing the same and use thereof

Info

Publication number: WO2008145389A2
Application number: PCT/EP2008/004329
Authority: WO
Inventors: Alfred Hagemeyer; Gerhard Mestl; Peter Scheck; Alice Kyriopoulos
Original assignee: Süd-Chemie AG
Priority date: 2007-05-31
Filing date: 2008-05-30
Publication date: 2008-12-04
Also published as: DE102007025444A1; JP2010527778A; CN101730584A; WO2008145389A3; JP5476293B2; KR20100031702A; EP2155380A2; US20100197956A1

Abstract

The invention relates to a shell catalyst for producing vinyl acetate monomer (VAM). Said shell catalyst comprises a porous catalyst support which is based on a natural phyllosilicate, especially on an acid-treated calcined bentonite, and which is loaded with Pd and Au. In order to provide a shell catalyst for use in the production of VAM which is characterized by a relatively high VAM selectivity and high activity, the catalyst support has a surface of less than 130 m2/g.

Description

VAM shell catalyst, process for its preparation and its use

The present invention relates to a coated catalyst for the production of vinyl acetate monomer (VAM) comprising a loaded with Pd and Au, porous, formed as a shaped catalyst support on the basis of a natural phyllosilicates, in particular based on an acid-treated calcined bentonite.

VAM is an important monomer building block in the synthesis of plastic polymers. The main application areas of VAM are i.a. the preparation of polyvinyl acetate, polyvinyl alcohol and polyvinyl acetal and the co- and terpolymerization with other monomers such as ethylene, vinyl chloride, acrylate, maleate, fumarate and vinyl laurate.

VAM is predominantly produced in the gas phase from acetic acid and ethylene by reaction with oxygen, wherein the catalysts used for this synthesis preferably contain Pd and Au as active metals and a

Alkali metal component as a promoter, preferably potassium in the form of the acetate. In the Pd / Au system of these catalysts, the active metals Pd and Au are presumably not in the form of metal particles of the respective pure metal, but rather in the form of Pd / Au alloy particles of possibly different composition, although the presence of unalloyed particles is not excluded can. As an alternative to Au, for example, Cd or Ba may also be used as second active metal component. Currently, VAM is predominantly using so-called

Shell catalysts prepared in which the catalytically active metals of the catalyst are not completely penetrate the shaped as a shaped catalyst support, but rather only in a more or less wide, outer region (shell) of the catalyst carrier molded body are contained (see, this EP 565 952 Al, EP 634 214 A1, EP 634 209 A1 and EP 634 208 A1), while the areas of the carrier which lie further inwards are virtually free of noble metal. With the help of shell catalysts, a more selective reaction is possible in many cases than with

Catalysts in which the carriers are impregnated ("impregnated") into the carrier core with the active components.

The shell catalysts known in the prior art for the production of VAM can be, for example, catalyst supports based on silica, alumina, aluminosilicate,

Titanium oxide or zirconium oxide (cf., for this purpose, EP 839 793 A1,

WO 1998/018553 A1, WO 2000/058008 A1 and WO 2005/061107 A1).

However, catalyst supports based on titanium oxide or zirconium oxide are currently scarcely used, since these

Catalyst carriers are not long-term stable to acetic acid and relatively expensive.

The majority of currently used catalysts for the preparation of VAM are coated catalysts with a Pd / Au shell on a porous, amorphous, formed as a ball aluminosilicate based on natural phyllosilicates, in particular on the basis of natural acid-treated calcined bentonites, with potassium acetate are impregnated as a promoter. Such VAM shell catalysts are usually prepared in a so-called chemical way in which the catalyst support with solutions of corresponding metal precursor compounds, for example by immersing the carrier in the solutions or by Incipient-Wetness method (pore filling method), in which the carrier with a is loaded with solution volume corresponding to its pore volume. The Pd / Au shell of the catalyst is produced, for example, by first impregnating the catalyst support molding in a first step with a Na ₂ PdCl ₄ solution and then in a second step the Pd component with NaOH solution on the catalyst support in the form a Pd hydroxide compound is fixed. In a subsequent, separate third step, the catalyst support is then impregnated with a NaAuClή solution and then the Au component also fixed by means of NaOH. After fixing the noble metal components in an outer shell of the catalyst support, the loaded catalyst support is then washed largely free of chloride and Na ions, then dried and finally reduced at 150 ^° C. with ethylene. The generated Pd / Au shell usually has a thickness of about 100 to 500 microns.

Usually, the catalyst carrier loaded with the noble metals is loaded with potassium acetate after the fixation or reduction step, wherein the loading with potassium acetate takes place not only in the outer, shell loaded with precious metals, but the catalyst support is completely impregnated with the promoter. The catalyst carrier used is predominantly a spherical carrier with the designation "KA-160" from SÜD-Chemie AG based on natural acid-treated bentonites as natural layered silicate, which has a BET surface area of about 160 m ² / g. The selectivities of VAM achieved by means of the known in the prior art VAM shell catalysts based on Pd and Au as active metals and KA-160 supports as catalyst support are about 90 mol .-% based on the supplied ethylene, wherein the remaining 10 mol .-% of the reaction products are essentially CO ₂ , which is formed by total oxidation of the organic starting materials / products.

An increase in VAM selectivity is desirable to reduce the cost of raw material losses and to make the work-up of the reaction product VAM simpler and thus more cost-effective.

The object of the present invention is therefore to provide a shell catalyst for the production of VAM, which is characterized by a relatively high VAM selectivity and high activity.

This object is achieved on the basis of a shell catalyst of the generic type in that the catalyst support has a surface area of less than 130 m ² / g.

The invention thus relates to a shell catalyst comprising a natural layered silicate, in particular an acid-treated calcined bentonite catalyst support molding having an outer shell, are contained in the metallic Pd and Au, wherein the catalyst support molded body has a BET surface area of less than 130 m ² / g. Shelled catalysts with a support in whose outer shell the active species has penetrated are also referred to in the art as "egg-shell" shell catalysts.

Surprisingly, it has been found that the coated catalyst according to the invention is characterized by a VAM selectivity increased by at least 1 mol% compared to the corresponding catalysts known in the prior art for the preparation of VAM. The increase in selectivity is essentially due to a decrease in the unwanted total oxidation of acetic acid, ethene and VAM to CO ₂ .

The catalyst according to the invention has an activity which is at least equal to that of the corresponding catalysts known in the prior art for the preparation of VAM. In addition, it was found that the activity of the catalyst according to the invention can be increased significantly by increasing the thickness of the Pd / Au shell, without having to accept significant losses in the VAM selectivity. In the case of the corresponding catalysts known in the prior art, an increase in the shell thickness is accompanied by a markedly reduced VAM selectivity.

In addition, despite its relatively low surface area, ie in spite of its relatively large pore volume, the catalyst according to the invention has excellent mechanical stability and exhibits high chemical resistance compared with the educts and products to be used and high thermal stability compared with the temperatures prevailing in VAM synthesis. If one leaves the reaction conditions in the technical use of the catalyst of the invention unchanged compared to a corresponding shell catalyst of the prior art, then more VAM per reactor volume and time can be produced, which is equivalent to an increase in capacity and additional investment. In addition, the work-up of the obtained Rohvinylacetats is facilitated because the VAM content in the product gas is higher, resulting in energy savings in the VAM workup. Suitable work-up procedures are disclosed, for example, in US Pat. No. 5,066,365 A and DE 29 45 913 A1.

On the other hand, if the VAM production capacity of a plant charged with the catalyst according to the invention is kept constant at the level of a corresponding known coated catalyst, then using the process according to the invention

Catalyst, the reaction temperature can be lowered, whereby a further increase in the VAM selectivity can be obtained with the aforementioned advantageous effects. This also reduces the proportion of CO ₂ produced as a by-product and therefore to be rejected and the entrainment loss associated with entrained ethylene. In addition, such a process management of a corresponding system due to lower temperatures leads to an extension of the catalyst life.

The term "on the basis of a natural layered silicate" as used herein means that the catalyst support molding comprises a natural layered silicate, wherein the natural layered silicate may be present in the catalyst support in both untreated and treated form Phyllosilicate before use as Carrier material may include, for example, treating with acids and / or calcining. The term "natural sheet silicate", for which the term "phyllosilicate" is also used in the literature, in the context of the present invention is understood to mean silicate mineral originating from natural sources, in which SiO ₄ tetrahedron, which is the basic structural unit of all silicates form, in layers of the general formula [Si ₂ O] ² are interlinked. ^"These tetrahedral layers alternate with so-called octahedron in which is a cation, especially Al and Mg, octahedrally coordinated by OH or surrounded 0th this case, for example, two-layer -Phyllosilikate and three-layer Phyllosilikate distinguished.

Phyllosilicates preferred in the context of the present invention are clay minerals, in particular kaolinite,

Beidellite, hectorite, saponite, nontronite, mica, vermiculite and smectites, with smectites and in particular montmorillonite being particularly preferred. Definitions of the term "sheet silicates" can be found, for example, in "Lehrbuch der anorganischen Chemie", Hollemann Wiberg, de

Gruyter, 102nd edition, 2007 (ISBN 978-3-11-017770-1) or in "Römpp Lexikon Chemie", 10th edition, Georg Thieme Verlag under the term "phyllosilicate". A particularly preferred natural layered silicate in the context of the present invention is a bentonite. Bentonites are not natural layer silicates in the actual sense, but rather a mixture of predominantly clay minerals, in which phyllosilicates are contained. In the present case, therefore, in the case where the natural sheet silicate is a bentonite, it is to be understood that the natural sheet silicate is present in the catalyst support in the form or as part of a bentonite. It has been found that the smaller the surface area of the catalyst support, the higher the VAM selectivity of the catalyst according to the invention. In addition, the smaller the surface area of the catalyst support, the greater the thickness of the Pd / Au shell can be, without causing significant losses of VAM selectivity. According to a preferred embodiment of the catalyst according to the invention, the surface of the catalyst support has a size of less than 125 m ² / g, preferably one of less than 120 m ² / g, preferably one of less than 100 m ² / g, more preferably one of less than 80 m ² / g and particularly preferably less than 65 m ² / g. In the context of the present invention, the term "surface area" of the catalyst support is understood to mean the BET surface area of the support, which is determined by adsorption of nitrogen in accordance with DIN 66132.

According to a further preferred embodiment of the catalyst according to the invention, it may be provided that the catalyst support has a surface area of between 130 and 40 m ² / g, preferably one of between 128 and 50 m ² / g, preferably one of between 126 and 50 m ² / g, more preferably one of between 125 and 50 m ² / g, more preferably one of between 120 and 50 m ² / g and most preferably one of between 100 and 60 m ² / g.

A formed as a shaped body catalyst support based on natural phyllosilicates, in particular based on an acid-treated calcined bentonite, wherein the catalyst support has a surface area of less than 130 m ² / g, preferably a surface area of between 130 and 40 m ² / g For example, be prepared by adding a acid-treated (uncalcined) bentonite as a layered silicate and water-containing molding mixture under compression a shaped body by means of those skilled in the art devices, such as extruders or tablet presses molded, and then the uncured molded body is calcined to form a stable shaped body. The size of the specific surface of the catalyst support depends in particular on the quality of the (bent) bentonite used, the acid treatment process of the bentonite used, ie, for example, the nature and relative to bentonite and the concentration of the inorganic acid used, the acid treatment time and -temperature, from

Compression pressure as well as the calcination time and temperature as well as the calcination atmosphere. A corresponding catalyst support with a surface area of about 100 m ² / g is offered by SÜD-Chemie AG under the name "KA-0".

Acid-treated bentonites can be obtained by treating bentonites with strong acids, such as sulfuric acid, phosphoric acid or hydrochloric acid. A definition of the term bentonite which also applies in the context of the present invention is given in Römpp, Lexikon

Chemie, 10th ed., Georg Thieme Verlag, stated. Bentonites which are particularly preferred in the context of the present invention are natural aluminum-containing sheet silicates which contain montmorillonite (as smectite) as the main mineral. After the acid treatment, the bentonite is usually washed with water, dried and ground to a powder.

The acidity of the catalyst support can advantageously influence the activity of the catalyst according to the invention in the gas-phase synthesis of VAM from acetic acid and ethene.

According to a further preferred embodiment of the catalyst according to the invention, the catalyst support has an acidity of between 1 and 150 μval / g, preferably one of between 5 and 130 μval / g, preferably one of between 10 and 100 μval / g and most preferably one of between 10 and 60 μval / g. The acidity of the catalyst support is determined as follows: 1 g of the finely ground catalyst support is mixed with 100 ml of water (with a pH blank value) and extracted with stirring for 15 minutes. It is then titrated with 0.01 N NaOH solution at least until pH 7.0, wherein the titration is carried out stepwise; Namely, 1 ml of the NaOH solution is added dropwise to the extract (1 drop / second), then waited 2 minutes, read the pH, 1 ml of NaOH is added dropwise, etc. The blank value of the water used is determined and the acidity Calculation corrected accordingly.

The titration curve (ml 0.01 NaOH versus pH) is then plotted and the point of intersection of the titration curve at pH 7 is determined. The molar equivalents are calculated in 10 ^{~ 6} equiv / g carriers, which result from the NaOH consumption for the point of intersection at pH 7.

Total acid: (10 * ml 0.01 N NaOH) / 1 carrier = μval / g

With regard to a low pore diffusion limitation, according to a further preferred embodiment of the catalyst according to the invention it can be provided that the catalyst support has an average pore diameter of 8 to 50 nm, preferably one of 10 to 35 nm and preferably one of 11 to 30 nm.

The catalyst according to the invention is usually prepared by subjecting a multiplicity of catalyst support shaped bodies to a "batch" process in whose individual process steps the shaped bodies are imparted, for example by stirring and mixing tools, to relatively high mechanical loads. In addition, the catalyst according to the invention can be mechanically stressed during the filling of a reactor, which can lead to an undesirable development of dust and damage to the catalyst support, in particular its located in an outer region, catalytically active shell. In particular, in order to keep the abrasion of the catalyst according to the invention within reasonable limits, the catalyst has a hardness greater than or equal to 20 N, preferably greater than or equal to 25 N, more preferably greater than or equal to 35 N, and most preferably one of greater than or equal to 40 N. The hardness is determined by means of a tablet hardness tester 8M from Dr. Ing. Schleuniger Pharmatron AG to 99 pieces of coated catalysts as an average determined after drying the catalyst at 130 ° C for 2h, the device settings are as follows:

Hardness: N

Distance to the molded body: 5.00 mm

Time delay: 0.80 s

Feed type: 6 D

Speed: 0.60 mm / s

The hardness of the catalyst or catalyst support can be influenced, for example, by varying certain parameters of the process for its preparation, for example by selecting the phyllosilicate, the calcination time and / or the calcination temperature of an uncured molding formed from a corresponding support mixture, or by certain additives such as for example, methyl cellulose or magnesium stearate. The catalyst according to the invention comprises a catalyst support based on a natural sheet silicate, in particular based on an acid-treated calcined bentonite. The term "on the basis" means in the context of the present invention that the catalyst comprises a natural layered silicate.

It may be preferred if the proportion of the catalyst support to phyllosilicate, in particular to acid-treated calcined bentonite, is greater than or equal to 50% by mass, preferably greater than or equal to 60% by mass, preferably greater than or equal to 70% by mass preferably greater than or equal to 80% by mass, more preferably greater than or equal to 90% by mass and most preferably greater than or equal to 95% by mass, based on the mass of the catalyst support.

It was found that the VAM selectivity of the catalyst according to the invention is dependent on the integral pore volume of the catalyst support. It is preferred if the catalyst support has an integral pore volume to BJH of between 0.25 and 0.7 ml / g, preferably one of between 0.3 and 0.6 ml / g and preferably one of 0.35 to 0, 5 ml / g. The integral pore volume of the catalyst support is determined by the method of BJH by means of nitrogen adsorption. The surface of the catalyst support and its integral pore volume are determined by the BET method or by the BJH method. The

Determination of the BET surface area according to the BET method according to DIN 66131; a publication of the BET method can also be found in J. Am. Chem. Soc. 60, 309 (1938). To determine the surface area and the integral pore volume of the catalyst support or of the catalyst, the sample can be used, for example, with a fully automatic nitrogen porosimeter from Micromeritics, type ASAP 2010 be measured, by means of which an adsorption and desorption isotherm is recorded.

To determine the surface area and the porosity of the catalyst support or of the catalyst according to the BET theory, the data are evaluated in accordance with DIN 66131. The pore volume is determined from the measurement data using the BJH method (E.P. Barret, L.J. Joiner, P.P. Haienda, J. Am. Chem. Soc. 73 (1951, 373)). This procedure also takes into account effects of capillary condensation. Pore volumes of certain pore size ranges are determined by summing up incremental pore volumes, which are obtained from the evaluation of the adsorption isotherm according to BJH. The integral pore volume according to the BJH method refers to pores with a diameter of 1.7 to 300 nm.

According to a further preferred embodiment of the catalyst according to the invention, it may be provided that the water absorbency of the catalyst support is 40 to 75%, preferably 50 to 70% calculated as weight increase by water absorption. The absorbency is determined by soaking 10 g of the carrier sample with deionized water for 30 minutes until no more gas bubbles escape from the carrier sample. Then, the excess water is decanted and the soaked sample is blotted with a cotton cloth to free the sample from adherent moisture. Then the water-loaded carrier is weighed and the absorbency calculated according to:

(Weight (g) - weight (g)) x 10 = water absorbency (%)

According to a further preferred embodiment of the catalyst according to the invention, it may be preferred if at least 80% of the integral pore volume of the Catalyst carrier according to BJH are formed by mesopores and macropores, preferably at least 85% and preferably at least 90%. This counteracts a reduced activity of the catalyst according to the invention caused by diffusion limitation, in particular in the case of Pd / Au shells with relatively large thicknesses. In this regard, the terms micropores, mesopores and macropores are understood to mean pores having a diameter of less than 2 nm, a diameter of 2 to 50 nm and a diameter of greater than 50 nm.

The catalyst support of the catalyst according to the invention may have a bulk density of more than 0.3 g / ml, preferably greater than 0.35 g / ml and more preferably a bulk density of between 0.35 and 0.6 g / ml.

In order to ensure sufficient chemical resistance of the catalyst according to the invention, the natural phyllosilicate present in the carrier has an SiO ₂ content of at least 65% by mass, preferably at least 80% by mass and preferably from 95 to 99.5% Mass .-% based on the mass of the layered silicate.

In the gas-phase synthesis of VAM from acetic acid and ethene, a relatively low Al ₂ O ₃ content in the layered silicate has little adverse effect, while at high Al ₂ O ₃

Maintained with a noticeable decrease in the pressure hardness must be expected. According to a preferred embodiment of the catalyst according to the invention, the phyllosilicate therefore contains less than 10% by weight of Al ₂ O ₃ , preferably 0.1 to 3% by mass and preferably 0.3 to 1.0% by mass, based on the mass of the phyllosilicate. The catalyst support of the catalyst according to the invention is formed as a shaped body. In this case, the catalyst support can basically take the form of any geometric body on which a corresponding noble metal shell can be applied. However, it is preferred if the catalyst support as a ball, cylinder (also with rounded faces), perforated cylinder (also with rounded faces), trilobus, "capped tablet", tetralobus, ring, donut, star, cartwheel, "inverse" cartwheel, or as a strand, preferably as Rippstrang or star train, is formed, preferably as a ball.

The diameter or the length and thickness of the

Catalyst support of the catalyst according to the invention is preferably 2 to 9 mm, depending on the geometry of the reactor tube in which the catalyst is to be used. If the catalyst support is designed as a sphere, then the catalyst support preferably has a diameter of greater than 2 mm, preferably a diameter of greater than 3 mm and preferably a diameter of 4 mm to 9 mm.

In order to increase the activity of the catalyst according to the invention, it may be provided that the catalyst support is doped with at least one oxide of a metal selected from the group consisting of Zr, Hf, Ti, Nb, Ta, W, Mg, Re, Y and Fe, preferably with ZrO ₂ , HfO ₂ or Fe ₂ Os. It may be preferred if the proportion of the catalyst support to doping oxide is between 0.01 and 20 mass%, preferably 1.0 to 10 mass% and preferably 3 to 8 mass%, based on the mass of the catalyst support , The amount of doping oxide depends primarily on the nature of the doping oxide to be used. In general, the smaller the thickness of the Pd / Au shell of the catalyst, the higher the VAM selectivity of the catalyst according to the invention. According to a further preferred embodiment of the catalyst according to the invention, therefore, the shell of the catalyst has a thickness of less than 300 microns, preferably one of less than 200 microns, preferably one of less than 150 microns, more preferably one of less than 100 microns, and more preferably one smaller than 80 μm. The thickness of the shell can be optically measured by means of a microscope. Indeed, the area where the precious metals are deposited appears black, while the non-precious areas appear white. The borderline between precious metal-containing and -free areas is usually very sharp and visually clearly visible. If the abovementioned boundary line is not sharp and can not be clearly identified, the thickness of the shell corresponds to the thickness of a shell, measured from the outer surface of the catalyst support, in which 95% of the precious metal deposited on the support is contained.

However, it has also been found that in the catalyst according to the invention the Pd / Au shell (as a function of the BET surface area of the support) can be formed with a relatively large thickness causing a high activity of the catalyst, without any appreciable reduction of the catalyst To effect VAM selectivity of the catalyst of the invention. In this case, the thickness of the noble metal shell can increase in thickness approximately inversely proportional to the BET surface area of the catalyst support. According to another preferred embodiment of the catalyst according to the invention, the shell of the catalyst therefore has a thickness of between 200 and 2000 microns, preferably one of between 250 and 1800 microns, preferably one of between 300 and 1500 microns, and more preferably one of between 400 and 1200 microns.

In order to ensure a sufficient activity of the catalyst according to the invention, the proportion of the catalyst in Pd is 0.6 to 2.5 mass%, preferably 0.7 to 2.3 mass% and preferably 0.8 to 2 mass. % based on the mass of the noble metal-loaded catalyst support.

Furthermore, it may be preferred for the catalyst according to the invention to have a Pd content of from 1 to 20 g / l, preferably from 2 to 15 g / l and preferably from 3 to 10 g / l.

Also to ensure sufficient activity and selectivity of the catalyst of the invention, that is

Au / Pd atomic ratio of the catalyst preferably between 0 and 1.2, preferably between 0.1 and 1, preferably between 0.3 and 0.9 and particularly preferably between 0.4 and 0.8.

Moreover, it may be preferable if the Au content of the catalyst of the present invention is from 1 to 20 g / L, preferably from 1.5 to 15 g / L, and preferably from 2 to 10 g / L.

In order to ensure a largely uniform activity of the catalyst according to the invention across the thickness of the Pd / Au shell, the noble metal concentration should vary only relatively little over the shell thickness. That is, the profile of the noble metal concentration of the catalyst is over a range of 90% of the shell thickness, with the range to the outer and inner

Each shell edge is separated by 5% of the shell thickness, from the average noble metal concentration of this range a maximum of +/- 20% off, preferably by a maximum of +/- 15% and preferably by a maximum of +/- 10%.

Chloride poisoned the catalyst of the invention and leads to a deactivation of the same. According to a further preferred embodiment of the catalyst according to the invention, therefore, its content of chloride is less than 250 ppm, preferably less than 150 ppm.

The catalyst according to the invention may be used in addition to or as an alternative to the abovementioned doping oxides as further

Promoter at least one alkali metal compound, preferably a potassium, a sodium, a cesium or a rubidium compound, preferably a potassium compound. Suitable and particularly preferred potassium compounds include potassium acetate KOAc, potassium carbonate K ₂ CO ₃ , potassium formate KFA, potassium hydrogen carbonate KHCO ₃ and potassium hydroxide KOH, and all potassium compounds which convert to K-acetate KOAc under the respective reaction conditions of VAM synthesis. The potassium compound can be applied both before and after the reduction of the metal components to the metals Pd and Au on the catalyst support. According to a further preferred embodiment of the catalyst according to the invention, the catalyst comprises an alkali metal acetate, preferably potassium acetate. It is particularly preferred for ensuring a sufficient promoter activity when the content of the catalyst of alkali metal acetate is 0.1 to 0.7 mol / 1, preferably 0.3 to 0.5 mol / 1.

According to a further preferred embodiment of the catalyst according to the invention, the alkali metal / Pd atomic ratio is between 1 and 12, preferably between 2 and 10 and more preferably between 4 and 9. The alkali metal / Pd atomic ratio is preferably the same smaller, the smaller the surface of the catalyst support.

The present invention furthermore relates to a first process for preparing a coated catalyst, in particular the coated catalyst according to the invention, comprising the steps:

a) providing a porous, designed as a shaped catalyst support on the basis of a natural phyllosilicate, especially on the basis of an acid-treated calcined bentonite, wherein the

Catalyst support has a surface area of less than 130 m ² / g;

b) applying a solution of a Pd precursor compound to the catalyst support;

c) applying a solution of an Au precursor compound to the catalyst support;

d) converting the Pd component of the Pd precursor compound into the metallic form;

e) converting the Au component of the Au precursor compound into the metallic form.

In principle, any Pd or Au compound which can be used to achieve a high degree of dispersion of the metals can be used as the Pd and Au precursor compounds. The term "degree of dispersion" is understood to mean the ratio of the number of all surface metal atoms of all metal / alloy particles of a supported metal catalyst to the total number of all metal atoms of the metal / alloy particles corresponds to relatively high numerical value, since in this case as many metal atoms are freely accessible for a catalytic reaction. That is, with a relatively high degree of dispersion of a supported metal catalyst, a certain catalytic activity thereof can be achieved with a relatively small amount of metal used. According to a further preferred embodiment of the catalyst according to the invention, the degree of dispersion of the paladium is 1 to 30%.

It may be preferred for the Pd and Au precursor compounds to be selected from the halides, in particular chlorides, oxides, nitrates, nitrites, formates, propionates, oxalates, acetates, hydroxides, bicarbonates, amine complexes or organic complexes, for example triphenylphosphine complexes or acetylacetonate complexes, these metals.

Examples of preferred Pd precursor compounds are water-soluble Pd salts. According to a particularly preferred embodiment of the method according to the invention, the Pd precursor compound is selected from the group consisting of Pd (NH ₃ J ₄ (OH) ₂ , Pd (NH ₃ J ₄ (OAc) ₂ , H ₂ PdCl ₄ , Pd (NH ₃ ) ₄ (HCO ₃ ) ₂ , Pd (NH ₃ ) ₄ (HPO ₄ ), Pd (NH ₃ J ₄ Cl ₂ , Pd (NH ₃ ) ₄ -xalate, Pd-oxalate, Pd (NO ₃ J ₂ , Pd ( NH ₃ ) ₄ (NO ₃ ) ₂ , K ₂ Pd (OAc) ₂ (OH) ₂ , Na ₂ Pd (OAc) ₂ (OH) ₂ , Pd (NH ₃ J ₂ (NO ₂ ) ₂ , K ₂ Pd (NO ₂ J ₄ , Na ₂ Pd (NO ₂ J ₄ , Pd (OAc) ₂ , K ₂ PdCl ₄ , (NH ₄ J ₂ PdCl ₄ , PdCl ₂ and Na ₂ PdCl ₄ , mixtures of two or more of the abovementioned salts Instead of NH ₃ as ligand, it is also possible to use ethylenamine or ethanolamine as ligand In addition to Pd (OAc) ₂ , other carboxylates of palladium may also be used, preferably the salts of aliphatic monocarboxylic acids having 3 to 5 carbon atoms, for example the propionate - or the butyrate salt. According to a further preferred embodiment of the method according to the invention, Pd nitrite precursor compounds may also be preferred. Preferred Pd nitrite precursor compounds are, for example, those obtained by dissolving Pd (OAc) 2 in a NaNO ₂ solution.

Examples of preferred Au precursor compounds are water-soluble Au salts. According to a particularly preferred embodiment of the method according to the invention, the Au precursor compound is selected from the group consisting of KAuO ₂ , HAuCl ₄ , KAu (NO ₂ ) 4, NaAu (NO ₂ J ₄ , AuCl ₃ , NaAuCl ₄ , KAuCl ₄ , KAu ( OAc) ₃ (OH), HAu (NO ₃ J ₄ , NaAuO ₂ , NMe ₄ AuO ₂ , RbAuO ₂ , CsAuO ₂ , NaAu (OAc) ₃ (OH), RbAu (OAc) ₃ OH, CsAu (OAc) ₃ OH , NMe ₄ Au (OAc) ₃ 0H and Au (OAc) _3. It may be advisable to use the Au (OAc) ₃ or KAuO ₂ by precipitating the oxide / hydroxide from a solution of gold acid, washing and isolating the precipitate, and Include the same in acetic acid or KOH each fresh.

Suitable solvents for the precursor compounds are all pure solvents or solvent mixtures in which the selected precursor compounds are soluble and, after application to the catalyst support, can easily be removed therefrom by drying. Preferred solvent examples of the metal acetates as precursor compounds are above all unsubstituted carboxylic acids, in particular acetic acid, or acetone, and for the metal chlorides especially water or dilute hydrochloric acid.

If the precursor compounds are not sufficiently soluble in acetic acid, water or dilute hydrochloric acid or mixtures thereof, alternatively or in addition to the solvents mentioned, other solvents may also be used Find. As other solvents here are preferably those solvents which are inert and are miscible with acetic acid or water. Preferred solvents which are suitable as an additive to acetic acid are ketones, for example acetone or acetylacetone, furthermore ethers, for example tetrahydrofuran or dioxane,

Acetonitrile, dimethylformamide and solvents based on hydrocarbons such as benzene called.

Preferred solvents or additives which are suitable as an additive to water are ketones, for example acetone, or alcohols, for example ethanol or isopropanol or methoxyethanol, alkalis, such as aqueous KOH or NaOH, or organic acids, such as acetic acid, formic acid, citric acid, tartaric acid , Malic acid, glyoxylic acid, glycolic acid, oxalic acid, pyruvic acid, oxamic acid, lactic acid or amino acids such as glycine.

If chloride compounds are used as precursor compounds, it must be ensured that the chloride ions are reduced to a tolerable residual amount before use of the catalyst prepared by the process according to the invention, since chloride is a catalyst poison. For this purpose, the catalyst support is usually washed extensively with water after fixing the Pd and Au components of the Pd or Au precursor compound on the catalyst support. This is generally done either immediately after fixation by hydroxide precipitation of the Pd and Au components by means of caustic or after reduction of the precious metal components to the respective metal / alloy.

According to a preferred embodiment of the method according to the invention, however, chloride-free Pd and Au precursor compounds are used and chloride-free Solvent to keep the content of the catalyst of chloride as low as possible and to avoid a complex chloride-free washing. The corresponding acetate, hydroxide, nitrite compounds or bicarbonate compounds are preferably used as precursor compounds, since these only contaminate the catalyst support with chloride to a very small extent.

The deposition of the Pd and Au precursor compounds onto the catalyst support in the region of an outer shell of the catalyst support can be achieved by processes known per se. Thus, the precursor solutions may be applied by impregnation by immersing the support in the precursor solutions or soaking in accordance with the incipient wetness method. Subsequently, a base, for example sodium hydroxide solution or potassium hydroxide solution, is applied to the catalyst support, whereby the noble metal components in the form of hydroxides are precipitated onto the support. For example, it is also possible first to impregnate the carrier with caustic and then to apply the precursor compounds to the carrier pretreated in this way.

According to a further preferred embodiment of the method according to the invention, it is therefore provided that the Pd and the Au precursor compound is applied to the catalyst support by the catalyst support with the solution of the Pd precursor compound and with the solution of the Au precursor compound or with a solution impregnated with both the Pd and Au precursor compounds.

According to the prior art, the active metals Pd and Au are applied starting from chloride compounds in the region of a shell of the support on the same by means of impregnation. However, this technique has reached its limits, which is minimal Shell thickness and maximum Au loading. The smallest shell thicknesses of the corresponding known VAM catalysts are at best about 100 microns and it is not foreseeable that even thinner shells can be obtained by impregnation. In addition, higher Au loadings within the desired shell by impregnation are difficult to realize because the Au precursor compounds tend to diffuse from the shell to inner zones of the catalyst support body, resulting in wide Au shells that are scarcely in regions mixed with Pd.

The active metals or their precursor compounds, for example, can also be applied to the carrier by means of so-called physical methods. For this purpose, the support according to the invention can preferably be sprayed, for example, with a solution of the precursor compounds, the catalyst support being moved in a coating drum into which warm air is blown in so that the solvent evaporates rapidly.

According to a particularly preferred embodiment of the method according to the invention, it is provided that the solution of the Pd precursor compound and the solution of Au precursor compound is applied to the catalyst support by the solutions are sprayed onto a fluidized bed or a fluidized bed of the catalyst support, preferably by means of a Aerosols of solutions. In the fluidized bed, the shaped bodies preferably run around elliptically or toroidally. To give an idea of how the moldings move in such fluid beds, it should be stated that in an "elliptical orbit" the

Move catalyst support moldings in the fluidized bed in a vertical plane on an elliptical orbit of varying size of the major and minor axis. In "toroidal circulation" The catalyst support moldings in the fluidized bed move in a vertical plane on an elliptical orbit of varying major sizes of the major and minor axes and in a horizontal plane on a circular path of varying magnitude of radius. On average, in the case of "elliptical circulation", the shaped bodies move in a vertical plane on an elliptical path, in "toroidal circulation" on a toroidal path, ie a shaped body helically moves off the surface of a torus with a vertically elliptical section. As a result, the shell thickness can be adjusted continuously and optimized, for example up to a thickness of 2 mm. But even very thin shells with a thickness of less than 100 microns are possible.

The abovementioned embodiment of the method according to the invention can be achieved by means of a fluidized bed system or

Fluid bed system can be performed. Particularly preferred is a fluidized bed system in which there is a so-called controlled Luftgleitschicht. On the one hand, the catalyst support moldings are well mixed by the controlled Luftgleitschicht while rotating about its own axis, whereby they are dried evenly from the process air. On the other hand, due to the consequent orbital movement of the shaped bodies caused by the controlled air sliding layer, the catalyst carrier shaped bodies pass the spraying process (application of the precursor compounds) in almost constant frequency. As a result, a substantially uniform shell thickness of a treated batch of moldings is achieved. Furthermore, it is achieved that the noble metal concentration varies only relatively small over a relatively large range of the shell thickness, ie, that the noble metal concentration over a large range of shell thickness is approximately a distorted rectangular function with high metal enrichment outside and slightly lower

Metal enrichment inside describes, whereby a largely uniform activity of the resulting catalyst is ensured across the thickness of the Pd / Au shell away.

Suitable dragee drums, fluidized bed plants or

Fluidized bed plants for carrying out the process according to the invention according to preferred embodiments are known in the art and are e.g. from the companies Heinrich Brucks GmbH (Alfeld, Germany), ERWEK GmbH (Heusenstamm, Germany), Stechel (Germany), DRIAM

Anlagenbau GmbH (Eriskirch, Germany), Glatt GmbH (Binzen, Germany), GS Divisione Verniciatura (Osteria, Italy), HOFER-Pharma Maschinen GmbH (Weil am Rhein, Germany), LB Bohle Maschinen + Verfahren GmbH (Enningerloh, Germany), Lödige Maschinenbau GmbH (Paderborn,

Germany), Manesty (Merseyside, UK), Vector Corporation (Marion, IA, USA), Aeromatic-Fielder AG (Bubendorf, Switzerland), GEA Process Engineering (Hampshire, UK), Fluid Air Inc. (Aurora, Ill., USA). , Heinen Systems GmbH (Varel, Germany), Hüttlin GmbH (Steinen, Germany), Umang Pharmatech Pvt. Ltd. (Marharashtra, India) and Innojet Technologies (Lörrach, Germany). Fluid bed devices made by Innojet named Innojet® Aircoater and Innojet® Ventilus are particularly preferred.

According to a further preferred embodiment of the method according to the invention, the catalyst support is heated during the application of the solutions, for example by means of heated process air. The degree of heating of the catalyst supports can be used to determine the drying rate of the applied solutions of the noble metal precursor compounds. At relatively low temperatures For example, the rate of desiccation is relatively low, so that, given a corresponding quantitative application, the formation of larger shell thicknesses may occur due to the high diffusion of the precursor compounds due to the presence of solvent. For example, at relatively high temperatures, the rate of desiccation is relatively high, so that solution of the precursor compounds coming into contact with the shaped article dries almost instantaneously, so solution applied to the catalyst support can not penetrate deeply into it. At relatively high

Temperatures can be obtained so relatively small shell thicknesses with high precious metal loading.

Commercially available solutions of the precursor compounds, such as Na ₂ PdCl ₄ , NaAuCl ₄ or HAuCl ₄ solutions, are usually used in the processes described in the prior art for the preparation of Pd-based VAM shell catalysts. In the recent literature, as already stated above, chloride-free Pd or Au precursor compounds such as Pd (NH ₃ J ₄ (OH) ₂ ,

Pd (NH ₃ ) ₂ (NO ₂ ) ₂ and KAuO ₂ used. These precursor compounds are basic in solution, while the classic chloride, nitrate, and acetate precursors all react acidically in solution.

For the application of the precursor compounds to the catalyst support, preference is usually given to using aqueous Na ₂ PdCl ₄ and NaAuCl ₃ solutions. These metal salt solutions are normally applied to the support at room temperature and then the metal components are fixed with NaOH as insoluble Pd or Au hydroxides. Thereafter, the loaded carrier is usually washed free of chloride with water. In particular, the Au fixation is with Disadvantages such as long exposure times of the base to induce the precipitation of the stable Au-Tetrachlorokomplexes, incomplete precipitation and associated poor Au retention.

According to a further preferred embodiment of the method according to the invention, the method comprises the steps:

a) providing a first solution of a Pd and / or an Au precursor compound; b) providing a second solution of a Pd and / or an Au precursor compound, wherein the first solution causes precipitation of the noble metal component (s) of the precursor compound (s) of the second solution, and vice versa; c) applying the first solution and the second solution to the catalyst support.

This embodiment of the method according to the invention uses two mutually different precursor solutions, one of which, for example, contains one Pd and the other an Au precursor compound. In this case, preferably one of the solutions has a basic and the other an acidic pH, as a rule. The application of the solutions to the catalyst support is usually carried out by first impregnating the support with the first and then, in a subsequent step, with the second solution as described above by impregnation. When applying the second solution, the two solutions are then combined on the support, whereby the pH of the solutions changes and the Pd or Au component of the respective precursor compound is precipitated on the support, without the need for a as in Conventional auxiliary base such as NaOH or KOH must be applied to the carrier.

The mentioned embodiment of the method according to the invention is thus based on an impregnation of the catalyst support with the first solution of a Pd and / or Au catalyst.

Precursor compound and the second solution of a Pd and / or Au precursor compound, wherein the two solutions are incompatible with each other, that is, that the first solution causes precipitation of the noble metal component (s) of the precursor compound (s) of the second solution and vice versa, so that in the

Both the preimpregnated Pd / Au component (s) and the postimpregnated Pd / Au component (s) precipitate almost simultaneously and thus lead to intimate Pd / Au mixing. Between the two impregnation steps can be optionally dried.

Suitable aqueous solutions of Pd precursor compounds for impregnation with incompatible solutions are listed by way of example in Table 1.

Table 1:

If NH ₃ should be too strongly reducing in terms of premature Au reduction, instead of Palladiumaminkomplexe also the corresponding diamine complexes with ethylenediamine as a ligand or the corresponding Ethanolaminkomplexe be used.

Suitable aqueous solutions of Au precursor compounds for impregnation with incompatible solutions are listed by way of example in Table 2.

Table 2:

Suitable combinations of incompatible solutions for base-free precipitation of the noble metal components are, for example, a PdCl ₂ and a KAuθ ₂ solution; a Pd (NO ₃ J ₂ and a KAuO ₂ solution; a Pd (NH ₃ J ₄ (OH) ₂ and an AuCl ₃ or HAuCl ₄ solution.

According to a further preferred embodiment of the method according to the invention, Pd can also be precipitated with incompatible Pd solutions and analogously Au with incompatible Au solutions, for example by contacting a PdCl ₂ solution with a Pd (NH ₃ ) ₄ (OH) ₂ solution or a HAuCl ₄ - with a KAuO ₂ solution. In this way, high Pd and / or Au Separate contents in the shell without having to use highly concentrated solutions.

According to a further embodiment of the method according to the invention, it is also possible to use mutually compatible mixed solutions which are brought into contact with the noble metal precipitate with a solution which is incompatible with the mixed solution. An example of a mixed solution is a solution containing PdCl ₂ and AuCl ₃ , whose noble metal components can be precipitated with a KAuθ ₂ solution, or a solution containing Pd (NHa) ₄ (OH) ₂ and KAuO ₂ , their noble metal components can be precipitated with a solution containing PdCl ₂ and HAuCl ₄ . Another example of a mixed solution is the pair HAuCl ₄ and KAuO ₂ .

The impregnation with the incompatible solutions is preferably carried out by impregnation or by spray impregnation, wherein the incompatible solutions, for example, simultaneously sprayed by one (two-fluid nozzle) or multiple double nozzle (s) or simultaneously by means of two nozzles or nozzle groups or seguentiell by means of one or more nozzle (s) become.

Impregnation with the incompatible solutions may result in thinner shells due to the rapid immobilization (fixation) of the metallic components of the precursor compounds in the shell, and the concomitant shortened Pd and Au diffusion, than the conventional use of mutually compatible solutions. By means of the incompatible solutions, high noble metal contents in thin shells, improved metal retention, faster and more complete precipitation of the noble metals, the reduction of the interfering Na residual content of the carrier, the simultaneous fixation of Pd and Au in just one fixing step and the omission of NaOH. Costs and the NaOH handling and avoidance of mechanical weakening of the carrier can be achieved by contact with excess NaOH.

By means of impregnation with incompatible solutions, a single fixing step, which involves only the application of two incompatible solutions, allows larger noble metal contents to be deposited on the catalyst support than is possible with classical bases (NaOH) fixation.

In particular, by means of the principle of incompatible solutions, high Au contents can be easily achieved with an Au / Pd atomic ratio of 0.5 and more, which is highly desirable in terms of increasing VAM selectivity.

According to a further preferred embodiment of the method according to the invention, it is provided that after the Pd and / or the Au precursor compound has been applied to the catalyst support, the catalyst support is subjected to a fixing step for fixing the noble metal component (s) of the precursor compound. on the catalyst support. The fixation step may involve treatment of the carrier with caustic or acid, depending on whether the precursor compound is acidic or basic, or a

Calcination of the carrier for transferring the noble metal component / s in a hydroxide compound / s or in an oxide include. The fixing step can also be omitted and the noble metal components are reduced directly, for example by treatment with a reducing gas phase, for example ethylene, etc. at elevated temperatures of 20 ⁰ C to 200 ⁰ C. By an intermediate calcination step, the Pd and / or Au precursor compounds are converted into the oxides and thereby fixed.

It is likewise possible to initially charge a support material based on a layered silicate as a powder and to impregnate it with the precursor compounds of the active metals. The pretreated powder can then be applied in the form of a "washcoat" to a suitable carrier structure, for example a ball of steatite or a KA-160 carrier, preferably by means of a coating drum, and then further processed by calcination and reduction to give the catalyst.

Accordingly, the invention relates to a second process for the preparation of a shell catalyst, in particular a shell catalyst according to the invention, comprising the steps:

a) providing a powdery porous carrier material based on a natural layered silicate, in particular based on an acid-treated calcined bentonite, wherein the carrier material with a Pd and an Au

Precursor compound or is loaded with Pd and Au particles and has a surface area of less than 130 m ² / g;

b) applying the loaded catalyst support to a support structure in the form of a shell;

c) calcining the loaded support structure from step b);

d), optionally, converting the Pd and the Au component of the Pd or Au precursor compound into the metallic form. Alternatively, the said method can also be carried out by first applying the non-noble-loaded, powdery carrier material to a carrier structure and only then applying the noble metals.

Directly after loading with the precursor compounds or after fixing the noble metal components, the support for calcining the noble metal components into the corresponding oxides can be calcined. The calcination is preferably carried out at temperatures of less than 700 ⁰ C. Particularly preferably between 300-450 ⁰ C with access of air. The calcination time depends on the calcination temperature and is preferably chosen in the range of 0.5-6 hours. At a calcination temperature of about 400 ^° C., the calcination time is preferably 1-2 hours. At a calcination temperature of 300 ^° C., the calcination time is preferably up to 6 hours. It can also be dispensed with the precipitation fixation and the impregnated salts can be directly calcined for the conversion of the metal component into an oxide. A preferred embodiment comprises calcining the Pd-laden carrier (with or without prior precipitation fixation) at about 400 ⁰ C to PdO formation followed by Au application and reduction in the (intermediate) to form a Au-sintering avoided can be.

The noble metal components are reduced before the use of the catalyst, wherein the reduction in situ, ie in the process reactor, or ex situ, ie in a special reduction reactor, can be performed. The reduction in situ is preferably carried out with ethylene (5% by volume) in nitrogen at a temperature of about 150 ^° C. over a period of, for example, 5 hours. The reduction ex situ For example, with 5% by volume of hydrogen in nitrogen, for example by means of forming gas, at temperatures in the range of preferably 150-500 ° C over a period of 5 hours.

Gaseous or volatilizable reducing agents such as CO, NH ₃ , formaldehyde, methanol and hydrocarbons may also be employed, which gaseous reducing agents may also be diluted with inert gas such as carbon dioxide, nitrogen or argon. Preferably, an inert gas is diluted

Reducing agent used. Preference is given to mixtures of hydrogen with nitrogen or argon, preferably with a hydrogen content of between 1% by volume and 15% by volume.

The reduction of the noble metals can also be carried out in the liquid phase, preferably by means of the reducing agents hydrazine, K-formate, Na-formate, ammonium formate, formic acid, K-hypophosphite, hypophosphorous acid, H ₂ O ₂ or Na hypophosphite.

The amount of reducing agent is preferably selected so that at least the equivalent necessary for complete reduction of the noble metal components is passed over the catalyst during the treatment period. Preferably, however, an excess of reducing agent is passed over the catalyst to ensure rapid and complete reduction.

Preferably, it is depressurized, ie at an absolute pressure of about 1 bar, reduced. For the production of industrial quantities of catalyst according to the invention, preference is given to a rotary kiln or a fluidized bed reactor or a fluidized bed reactor used to ensure a uniform reduction of the catalyst.

The invention furthermore relates to the use of the catalyst according to the invention as oxidation catalyst, as hydrogenation / dehydrogenation catalyst, as catalyst in hydrodesulfurization, as hydrodenitrification catalyst, as hydrodeoxigenation catalyst or as catalyst in the synthesis of alkenylalkanoates, in particular in the synthesis of vinyl acetate monomer, especially in the gas phase oxidation of ethylene and acetic acid to vinyl acetate monomer.

The catalyst according to the invention is preferably used for the production of VAM. This is generally done by passing acetic acid, ethylene and oxygen or

Oxygen-containing gases at temperatures of 100-200 ⁰ C, preferably 120-200 ⁰ C, and at pressures of 1-25 bar, preferably 1-20 bar, over the catalyst according to the invention, wherein unreacted starting materials can be recycled. It is expedient to keep the oxygen concentration below 10% by volume. Under certain circumstances, however, a dilution with inert gases such as nitrogen or carbon dioxide is advantageous. In particular, carbon dioxide is suitable for dilution since it is formed in small amounts in the course of VAM synthesis. The resulting vinyl acetate is isolated by suitable methods described, for example, in US 5,066,365 A.

The following embodiments serve in connection with the comparative example of the explanation of the invention:

Example 1: 225 g of spherical, formed from an acid-treated calcined bentonite as a natural sheet silicate catalyst support molding from SÜD-Chemie AG (Munich, Germany) with the trade name "KA-0" and the characteristics listed in Table 3:

Table 3:

were in a fluidized bed apparatus of the company Innojet Technologies (Lörrach, Germany) filled with the trade name Innojet® Aircoater and mixed by means of compressed air at 80 ⁰ C compressed air (6 bar) in a fluidized bed state in which the shaped bodies toroidal, ie on a vertically oriented ellipsoids and a vertically oriented horizontal circular path moved.

After the moldings had been heated to a temperature of about 75 ^° C., 300 ml of an aqueous noble metal mixed solution containing 7.5 g of commercially available Na ₂ PdCl ₄ (sodium tetrachloropalladate) and 4.6 g of commercially available NaAuCl ₄ (sodium tetrachloroaurate) were placed on the fluidized bed of the moldings. sprayed over a period of 40 min.

After impregnation of the catalyst support with the

Precious metal mixed solution was sprayed onto the fluidized bed of the moldings a 0.05 molar NaOH solution at a temperature of 80 ° C over a period of 30 min. In the process, the NaOH precipitates predominantly within the shell and fixes the Pd and Au metal components without exposing the support to excessively high NaOH concentrations.

After NaOH exposure, the supports were washed extensively with water in the fluidized bed apparatus to substantially free the support from alkali metal and chloride introduced into the support via the noble metal compounds and NaOH.

After washing, the moldings were dried by moving in hot process air (100 ^° C.) in the fluidized bed apparatus.

After drying the moldings, they were reduced to a Pd / Au coated catalyst with a gas mixture of ethylene (5% by volume) in nitrogen at a temperature of about 150 ^° C. in the fluidized bed apparatus.

The resulting coated catalyst contained about 1.2 mass% Pd and had an Au / Pd atomic ratio of about 0.5, a shell thickness of about 160 microns and a hardness of 38 N. The noble metal concentration of the Pd / Au coated catalyst thus produced deviated over a range of 90% of the shell thickness, with the outer and inner shell boundary areas each spaced 5% of the shell thickness, from the average noble metal concentration of this region by a maximum of +/- 10 % off. The determination of the noble metal distribution was carried out on a scanning electron microscope LEO 430VP, equipped with an energy-dispersive spectrometer from Bruker AXS. To measure the noble metal concentration over the shell thickness, a catalyst ball was cut through, glued onto an aluminum sample holder and then vapor-deposited with carbon. As a detector, a nitrogen-free silicon drift chamber detector (XFlash® 410) was used with an energy resolution of 125 eV for the manganese K _a i _Pha ~ line.

Example 2

65.02 g of catalyst support shaped bodies "KA-0" as defined in Example 1 are mixed with 43.8 ml of an aqueous solution according to the incipient wetness method, in which a support having a solution volume corresponding to its pore volume is impregnated containing 1.568 g of Na ₂ PdCl ₄ and 0.367 g of HAuClή impregnated After the impregnation 89.17 g of a 0.35 molar NaOH solution to the

Catalyst support molded body and allowed to stand overnight at RT for 22 hours. After decanting the fixing solution, the catalyst precursor thus prepared is reduced with 73.68 g of a 10% NaH ₂ PO ₂ solution (Fluka) for 2 hours. After draining the reduction solution, the catalysts are washed with dist. Water for 8 hours at RT while constantly changing the water (flow = 140 rpm) to Washed removal of Cl residues. The final value of the conductivity of the washing solution is 1.2 μS.

The catalyst is then dried in the fluidized bed at 90 ^° C. for 50 minutes. The dried spheres are mixed with a mixture of 27.29 g 2 molar KOAc solution and 18.55 g

Loaded H ₂ O and allowed to stand for one hour at room temperature. At the end of the drying takes place for 40 min at 90 ⁰ C in the fluidized bed.

The theoretical metal loading is 0.8 wt% Pd and 0.3 wt% Au; The values experimentally determined by elemental analysis by ICP (Inductively Couples Plasma) were 0.77 wt% Pd and 0.27 wt% Au.

The shell thickness was 312 microns.

Comparative Example 1

A catalyst was prepared analogously to Example 2, with the catalyst support molding being a support from St) D-

Chemie AG under the trade designation "KA-160" having the characteristics listed in Table 4:

Table 4

In contrast to example 2, 39.1 ml of an aqueous solution containing 1.568 g of Na ₂ PdCl ₄ and 0.367 g of HAuCl _{4 were} impregnated.

The theoretical metal loading is 0.8 wt% Pd and 0.3 wt% Au; the values experimentally determined by elemental analysis by ICP were 0.78 wt% Pd and 0.27 wt% Au.

The shell thickness was 280 μm. Example 3

reactor test

6 ml of a bed of catalyst balls of Example 2 and Comparative Example 1 were each in a

Fixed bed tubular reactor at a temperature of 150 ⁰ C at 10 bar with a feed gas stream of 550 Nml / min composed of 15% HOAc, 6% O ₂ , 39% C ₂ H ₄ in N ₂ and analyzed the reactor effluent by gas chromatography.

The selectivity (of ethylene to VAM) is calculated by the formula S (C ₂ H ₄₎ = mole VAM / (mole VAM + mole CO _2/2). The space-time yield is given as g VAM / 1 catalyst / h. The oxygen conversion is calculated according to (mole O ₂ in-mole O ₂ out) / mole O ₂ in.

The inventive catalyst according to Example 2 shows a selectivity S (C ₂ H ₄ ) of 92.3% and a space-time yield (determined by gas chromatography) of 615 g VAM / 1 catalyst / h at an oxygen conversion of 36.5%.

The catalyst according to Comparative Example 1 showed a selectivity S (C ₂ H ₄ ) of 91.0% and a space-time yield (determined by gas chromatography) of 576 g VAM / 1 catalyst / h at an oxygen conversion of 36.1%.

The inventive catalyst according to Example 2 shows both a higher selectivity and activity in the VAM synthesis compared to a catalyst of the prior art according to Comparative Example 1.

Claims

claims

1. coated catalyst for the production of vinyl acetate monomer, comprising a loaded with Pd and Au porous, designed as a shaped catalyst support on the basis of a natural phyllosilicate, in particular on the

Base of an acid-treated calcined bentonite, wherein the catalyst support has a surface area of less than 130 m ² / g.

2. A catalyst according to claim 1, characterized in that the catalyst support has a surface area of less than 125 m ² / g, preferably a smaller than 120 m ² / g, preferably a smaller than 100 m ² / g, more preferably one of less than 80 m ² / g, and more preferably less than 65 m ² / g.

3. Catalyst according to one of the preceding claims, characterized in that the catalyst support has a surface area of between 130 and 40 m ² / g, preferably one of between 128 and 50 m ² / g, preferably one of between 126 and 50 m ² / g, more preferably one of between 125 and 50 m ² / g, more preferably one of between 120 and 50 m ² / g and most preferably one of between 100 and 60 m ² / g.

4. Catalyst according to one of the preceding claims, characterized in that the catalyst support has an acidity of between 1 and 150 μval / g, preferably one of between 5 and 130 μval / g, preferably one of between 10 and 100 μval / g and especially preferably one of between 10 and 60 μval / g.

5. Catalyst according to one of the preceding claims, characterized in that the catalyst support has a middle Pore diameter of 8 to 50 nm, preferably one of 10 to 35 nm, and preferably one of 11 to 30 nm.

6. Catalyst according to one of the preceding claims, characterized in that the catalyst has a hardness of greater than or equal to 20 N, preferably one of greater than or equal to 30 N, more preferably one of greater than or equal to 40 N and most preferably one of greater / equal to 50 N.

7. Catalyst according to one of the preceding claims, characterized in that the proportion of the catalyst support of natural phyllosilicate, in particular on acid-treated calcined bentonite, greater than or equal to 50 mass .-%, preferably greater than / equal to 60 mass .-%, preferably greater / is equal to 70% by mass, more preferably greater than or equal to 80% by mass, more preferably greater than or equal to 90% by mass, and most preferably greater than or equal to 95% by mass, based on the mass of the catalyst support.

8. Catalyst according to one of the preceding claims, characterized in that the catalyst support is an integral

Pore volume to BJH of between 0.25 and 0.7 ml / g, preferably one of between 0.3 and 0.6 ml / g and preferably one of 0.35 to 0.5 ml / g.

9. Catalyst according to one of the preceding claims, characterized in that at least 80% of the integral pore volume of the catalyst support of mesopores and macropores are formed, preferably at least 85% and preferably at least 90%.

10. Catalyst according to one of the preceding claims, characterized in that the catalyst support has a bulk density of more than 0.3 g / ml, preferably greater than 0.35 g / ml and most preferably a bulk density of between 0.35 and 0.6 g / ml.

11. Catalyst according to one of the preceding claims, characterized in that the phyllosilicate contained in the carrier has a SiO ₂ content of at least 65% by mass, preferably one of at least 80% by mass and preferably from 95 to 99.5% Mass .-%.

12. Catalyst according to one of the preceding claims, characterized in that the carrier contained in the

Phyllosilicate contains less than 10 mass% Al ₂ O ₃ , preferably 0.1 to 3 mass% and preferably 0.3 to 1.0 mass%.

13. Catalyst according to one of the preceding claims, characterized in that the catalyst support is designed as a sphere, cylinder, perforated cylinder, trilobus, ring, star or strand, preferably as a rib strand or star strand, preferably as a sphere.

14. Catalyst according to one of the preceding claims, characterized in that the catalyst support is designed as a ball with a diameter of greater than 2 mm, preferably with a diameter of greater than 3 mm and preferably with a diameter of greater than 4 mm.

15. Catalyst according to one of the preceding claims, characterized in that the catalyst support is doped with at least one oxide of a metal selected from the group consisting of Zr, Hf, Ti, Nb, Ta, W, Mg, Re, Y and Fe, preferably with ZrO ₂ , HfO ₂ or Fe ₂ Oa.

16. Catalyst according to claim 15, characterized in that the proportion of the catalyst support of doping oxide is between 0.01 and 20 mass%, preferably 1.0 to 10 mass% and preferably 3 to 8 mass%.

17. Catalyst according to one of the preceding claims, characterized in that the shell of the catalyst has a thickness of less than 300 microns, preferably one of less than 200 microns, preferably one of less than 150 microns, more preferably one of less than 100 microns and more preferably one smaller than 80 μm.

18. A catalyst according to any one of claims 1 to 16, characterized in that the shell of the catalyst has a thickness of between 200 and 2000 microns, preferably one of between 250 and 1800 microns, preferably one of between 300 and 1500 microns, and more preferably one from between 400 and 1200 μm.

19. Catalyst according to one of the preceding claims, characterized in that the proportion of the catalyst in Pd is 0.6 to 2.5 mass%, preferably 0.7 to 2.3 mass% and preferably 0.8 to 2 mass .-% based on the mass of the catalyst carrier loaded with noble metal.

20. Catalyst according to one of the preceding claims, characterized in that the Au / Pd atomic ratio of the catalyst is between 0 and 1.2, preferably between 0.1 and 1, preferably between 0.3 and 0.9 and more preferably between 0.4 and 0.8.

21. Catalyst according to one of the preceding claims, characterized in that the noble metal concentration of Catalyst over a range of 90% of the shell thickness, wherein the range to the outer and inner shell boundary each spaced by 5% of the shell thickness deviates from the mean noble metal concentration of this range by a maximum of +/- 20%, preferably by a maximum of +/- 15 % and preferably by a maximum of +/- 10%.

22. Catalyst according to one of the preceding claims, characterized in that the catalyst has a content of chloride of less than 250 ppm, preferably less than 150 ppm.

23. Catalyst according to one of the preceding claims, characterized in that the catalyst comprises an alkali metal acetate, preferably potassium acetate.

24. A catalyst according to claim 23, characterized in that the content of the catalyst of alkali metal acetate is 0.1 to 0.7 mol / 1, preferably 0.3 to 0.5 mol / 1.

25. Catalyst according to one of claims 23 to 24, characterized in that the alkali metal / Pd atomic ratio is between 1 and 12, preferably between 2 and 10 and preferably between 4 and 9.

26. A process for producing a coated catalyst, in particular a coated catalyst according to one of the preceding claims, comprising the steps:

a) providing a porous, designed as a shaped catalyst support on the basis of a natural phyllosilicate, especially on the basis of an acid-treated calcined bentonite, wherein the Catalyst support has a surface area of less than 130 m ² / g;

b) applying a solution of a Pd precursor compound to the catalyst support;

c) applying a solution of an Au precursor compound to the catalyst support;

27. The method according to claim 26, characterized in that the Pd and Au precursor compounds are selected from the halides, especially chlorides, oxides, nitrates, nitrites, formates, propionates, oxalates, acetates, hydroxides, bicarbonates, amine complexes or organic complexes, for example

Triphenylphosphine complexes or acetylacetonate complexes, these metals.

28. The method according to any one of the preceding claims, characterized in that the Pd precursor compound is selected from the group consisting of Pd (NH ₃₎ ₄ (OH) _2, Pd (NH ₃ J ₄ (OAc) _2, H ₂ PdCl ₄ , Pd (NH ₃ ) ₄ (HCO ₃ ) ₂ , Pd (NH ₃ J ₄ (HPO ₄ ), Pd (NH ₃ J ₄ Cl ₂ , Pd (NH ₃ ), oxalate, Pd (NO ₃ ) ₂ , Pd (NH ₃ ) ₄ (NO ₃ ) ₂ , K ₂ Pd (OAc) ₂ (OH) ₂ , Pd (NH ₃ ) ₂ (NO ₂ ) ₂ , K ₂ Pd (NO ₂ ) ₄ , Na ₂ Pd (NO ₂ J ₄ , Pd (OAc) ₂ , PdCl ₂ and Na ₂ PdCl ₄ .

29. The method according to any one of the preceding claims, characterized in that the Au precursor compound selected is selected from the group consisting of KAUO2, _HAuCl4, KAu (NO ₂₎ 4, AuCl _3, NaAuCl _4, KAu (OAc) ₃ (OH), HAu _(NO3) _4, NaAuO _2, NMe ₄ AuO _2, RbAuO ₂ , CsAuO ₂ , NaAu (OAc) ₃ (OH), RbAu (OAc) ₃ OH, CsAu (OAc) ₃ OH, NMe ₄ Au (OAc) ₃ OH, and Au (OAc) ₃ .

30. The method according to any one of the preceding claims, characterized in that the Pd and the Au precursor compound is applied to the catalyst support by the catalyst support with the solution of the Pd precursor compound and with the solution of the Au precursor compound or with a solution, which contains both the Pd and the Au precursor compound is soaked.

31. The method according to any one of claims 26 to 29, characterized in that the solution of the Pd precursor compound and the solution of the Au precursor compound on the

Catalyst support is applied by the solutions are sprayed onto a fluidized bed or a fluidized bed of the catalyst support, preferably by means of an aerosol of the solutions.

32. The method according to any one of the preceding claims, characterized in that the catalyst support is heated during the application of the solutions.

33. The method according to any one of the preceding claims, characterized in that

a) providing a first solution of a Pd and / or an Au precursor compound;

b) a second solution of a Pd and / or an Au precursor compound is provided, wherein the first solution is a precipitate of the noble metal component (s) of the Precursor compound / s causes the second solution and vice versa;

c) the first and the second solution is applied to the catalyst support.

34. The method according to claim 33, characterized in that the precursor compounds of one solution are acidic and those of the other solution are basic.

35. The method according to any one of the preceding claims, characterized in that the catalyst support, after the Pd and / or the Au precursor compound has been applied to the catalyst support / is subjected to a fixing step.

36. A process for producing a coated catalyst, in particular a coated catalyst according to one of the preceding claims, comprising the steps:

a) providing a powdery porous

Support material based on a natural layered silicate, in particular based on an acid-treated calcined bentonite, wherein the support material is loaded with a Pd and an Au precursor compound or with Pd and Au particles and a surface area of less than 130 m ² / g having;

b) applying the loaded carrier material to a support structure in the form of a shell;

c) calcining the loaded support structure from step b); d), optionally, converting the Pd and the Au component of the Pd or Au precursor compound into the metallic form.

37. Use of a catalyst according to any one of the preceding claims as an oxidation catalyst, as

Hydrogenation / dehydrogenation catalyst, as a catalyst in hydrodesulfurization, as Hydrodesoxigenierungs- catalyst, as Hydrodenitrifizierungskatalysator or as a catalyst in the synthesis of alkenylalkanoates, in particular in the synthesis of vinyl acetate monomer, in particular in the gas phase oxidation of ethylene and acetic acid to vinyl acetate monomer.